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Old 08-17-08, 09:10 PM   #1
mkmumf
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My rear derailer came off!!

I've got a Nishiki backroads aluminum mountain bike. Not a very high end bike ( 10 years ago it cost me $250) but it has done me well over the years. Recently while riding a small stick caught up in the rear derailer and the next thing I knew I was walking. It seems the stick bent the bracket the derailer mounts to right across the hole at not quite a 45 degree radiused angle. The derailer was pried from the bracket. The bike is all aluminum and it appears that there was a helicoil or some type of hard metal threading in the aluminum that came out with the derailer mounting bolt. Any suggestions for repair? I have found a thread repair kit for a metric 10 x 1.0 bolt. Will the aluminum take straightening and new threads inserted or will it be too brittle? Is it worth the time and effort? The local bike shop was not very interested in attempting a repair. There are some bigger shops in town I haven't checked with yet. What do you experienced guys think?
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Old 08-17-08, 09:13 PM   #2
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You can try straightening it and inserting a new helicoil. If that works put a new derailleur hanger on and you should be good to go. If it doesn't work, remember that Craigslist is your friend. You can find good deals on great bikes there if you don't quite have the scratch to drop on a new one from a shop.

Mike
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Old 08-17-08, 09:30 PM   #3
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I would be very surprised if the derailler mounting hole was Heli-coiled. More likely, the metal that came out with the bolt was the aluminum threads, meaning that the tapped hole is now stripped. Assuming you can straighten the frame, you will need to install a thread insert (Heli-coil or similar) in order to reinstall the derailler.

For straightening the frame, since it's aluminum it may crack when you try to bend it back. If it does, there's not much you can do to fix it that won't cost more than the frame is worth.
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Old 08-17-08, 09:32 PM   #4
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The derailleur hanger has to be bent back by a shop - they have a special tool for that. If the bolt hole is bent it seems unlikely to me it can be straightened and reinforced, but I'm not an expert. I think you're looking at a new bike.
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Old 08-17-08, 09:51 PM   #5
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If it bent right at the hole so that part of the threaded section is bent one way and the other part is another way then that hanger is toast. YOu'll never bend it back in such a way that the derrailleur will fit back in. Also being aluminium it will more likely crack the end off as you try to straighten it.

Now MOST aluminium frames used replaceable dropout hangers just for this reason. Look at your frame again to see if it has one of those. If it doesn't then it's new frame time.
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Old 08-17-08, 10:21 PM   #6
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(Man, you guys gotta get a life!!) Should of read... Man, you guys are awesome. I never expected to have quality responses from several members so quickly! Thanks for the replies!
I'm sure it is a one piece derailluer hanger with no dropout. Looks like that would be a good idea! There is some kind of thread material that is not aluminum that came out with the deraillure mounting bolt. I guess I'll order the repair kit and try to fix it but I agree it may be time for a new bike. Thanks for the info. The guy at the bike shop wanted to sell me a Giant Boulder SE (2008 model). $300 good?

Last edited by mkmumf; 08-18-08 at 06:51 AM.
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Old 08-17-08, 10:31 PM   #7
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I guess I'll order the repair kit and try to fix it
Even if you miraculously rethread the hole, the derailleur won't be lined up with the cogs and you will get skipping or autoshifting. However if the repair kit is cheap I guess there's no harm in trying. Try to bend the hanger straight before you mount the derailleur. If you use the derailleur as a lever to try to bend the frame you may damage the derailleur.
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Old 08-18-08, 12:43 AM   #8
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A trick that may help you with bending the aluminium back.... And this only works for bare aluminium so if it is painted then you're toast.

If you heat the metal to a certain point the stress hardening from the original bending will be relieved and you can bend the hanger back possibly without the hanger snapping off.

The trick is to blacken the metal with soot from a candle or a closely held Bic lighter flame. Make sure the metal is in the yellow part of the flame so you get the most blackening.

Then light up a propane torch and play the flame over the blackening until the black dissappears. Cool the metal either with air, time or water and then clamp on whatever you need to bend it back. It is now softer than it was and you can bend the part back to shape.

It works amazingly well. I've done a few motorcycle levers for off road bikes over the years and they all held up well after staightening. Normally they would snap when you try to bend them back straight.
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Old 08-18-08, 02:26 AM   #9
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Man, you guys gotta get a life!! Thanks for the replies!
Offend us then thank us? WTF?
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Old 08-18-08, 02:52 AM   #10
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There's two distinct ideas going on here. First is that "you" probably won't be able to bend back the hanger and have it be aligned correctly.

Second is that "it is possible" to get it fixed, but you'll need to find a qualifed shop that's familiar with the procedure. Of utmost importance is an alignment tool to verify that the hanger is straight. And yeah, they'll also have an insert kit to repair the threads. Helicoil is ghetto at best. Time-serts or EZ-lok is a much better choice.
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Old 08-18-08, 06:34 AM   #11
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Quote:
Originally Posted by mkmumf View Post
Man, you guys gotta get a life!! Thanks for the replies!
I'm sure it is a one piece derailluer hanger with no dropout. Looks like that would be a good idea! There is some kind of thread material that is not aluminum that came out with the deraillure mounting bolt.
I agree that this sounds like a rather gratuitous insult to those trying to provide the info you requested. Your manners need work.

If the threads that came out with the derailleur were steel, not aluminum, it's possible the derailleur hanger was repaired in the past with something like this:

http://www.biketoolsetc.com/index.cg...em_id=VR-130/1

Dealers commonly use them to repair damaged rd mounting holes or it might even be an OEM part to strengthen an inherently weak threaded hole.
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Old 08-18-08, 07:40 AM   #12
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I agree that this sounds like a rather gratuitous insult to those trying to provide the info you requested. Your manners need work.
I thought gratuitious insults were what we thrived on around here, kind of like the gratuitious nudity in Fast Times at Ridgemont High that makes the movie a classic (Phoebe Cates when I was in high school )
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Old 08-18-08, 08:04 AM   #13
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Firstly may I apologize again for my earlier crude and totally out of place statement regarding you guys. I can only assure you that the intentions were never intended to be taken in a negative manor.
Hillrider, that dropout repair kit ( http://www.biketoolsetc.com/index.cg...em_id=VR-130/1 ) looks like it would make an excellent repair. Probably stronger than the original installation. Have you had any experience with it?
I've attached a few pics of the damage and the insert that came out for your viewing pleasure.

Thanks
Attached Images
File Type: jpg deraillure mounting tab rear view.JPG (17.7 KB, 24 views)
File Type: jpg deraillure mount insert.JPG (14.8 KB, 16 views)
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Old 08-18-08, 08:32 AM   #14
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Take a look at the before and after derailer pictures of this aluminum framed Schwinn (subject of a previous post). The hanger was bent primarily at the mounting hole. I bent it back with an adjustable wrench. There was no indication of cracking or any failure in the material. I doubt that it would survive another bending but it's working fine, for now...

Better quality aluminum alloy might not take the abuse as well but it's certainly worth a try to straighten it. What have you got to lose?
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Old 08-18-08, 08:58 AM   #15
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Originally Posted by mkmumf View Post
Firstly may I apologize again for my earlier crude and totally out of place statement regarding you guys. I can only assure you that the intentions were never intended to be taken in a negative manor.
Hillrider, that dropout repair kit ( http://www.biketoolsetc.com/index.cg...em_id=VR-130/1 ) looks like it would make an excellent repair. Probably stronger than the original installation. Have you had any experience with it?
I've attached a few pics of the damage and the insert that came out for your viewing pleasure.

Thanks
Appology accepted. "Tone of Voice" doesn't translate very well over the internet does it?

I have no personal experience with these inserts (fortunately) but I have heard many reports that they work very well and, as I mentioned, are a commpn LBS repair technique. The inserts come in a couple of lengths depending on the dropout/hanger thickness being worked on. If you can adequately align your current hanger, one of these should get you back in business.
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Old 08-18-08, 03:33 PM   #16
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I've attached a few pics of the damage and the insert that came out for your viewing pleasure.
After viewing the picture, I stand corrected. That most certainly is a thread insert, likely from a previous repair. The issue you may run into now though is that since a previous repair has been done, material has already been removed to install the thread insert. You might not have enough material left in place to install a standard thread insert again. A machine shop should be able to make you a special insert that would do the trick though.
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Old 08-18-08, 04:53 PM   #17
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The bent hanger doesn't look that bad. Since the threads are already damaged, you don't have to worry about that. The shop can just bend/pound the hanger straight. Then install an insert. I recommend the 1-piece EZ-lok as it's much stronger than a Helicoil and thicker too, so the existing hole can be re-drilled and tapped. It comes with red permanent Loctite on the threads of the insert, and I recommend applying more on the fresh threads in the hanger. Finally they can align it as the final step of the repair.
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Old 08-18-08, 05:17 PM   #18
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thread........

dude this is a 75 dollar bike on craigslist..............dude take the bike to the shop--- have them use the proper alignment tool from park and heli it----dude............ Performance has a sale! 250.... new ride ---- safe ---- big breath!
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Old 08-18-08, 05:20 PM   #19
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wow

i have now looked at the pictures--- buy a new bike..... enjoy todays technology----
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Old 08-18-08, 07:29 PM   #20
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I don't think that's a helicoil, I think it's the spring from your derailleur. I'd be leery of bending an all-aluminum dropout, and would probably take it to the LBS, which I never do. Barring that, I think you now have yourself a single speed mountain bike. They're all the rage.
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Old 08-19-08, 11:26 AM   #21
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Thanks for all the info. I talked to a guy at bike tools etc and ordered the insert that Hillrider suggested. Should be here Fri. I'll let you know how it turns out. This seems the best choice as I can't determine the amount of material that came out with the threads and the finished product should be plenty strong. The repair should be the easy part. After reading about aligning the dropout bracket it looks like that will be the bigggest challenge.
I realize this isn't a high end bike and I actually found a Specialized Rockhopper for $95 but fixing this for about $8 will be a fun challenge and will get me where I need to go.
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Old 08-22-08, 09:20 PM   #22
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Well, a few hours of work and I'm back on the road! The insert was easy to install. I reformed the bracket before making any adjustments to the deraillure and it must be close cause it is shifting solid. Thanks for the tips!
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Old 08-22-08, 09:45 PM   #23
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Hey good job!
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